Current methods for assessing skeletal maturity in US children are inadequate both in terms of racial/ethnic representation and outdated samples. The United States is a multi-racial nation, yet skeletal maturity standards are based on white children from many generations ago. The primary goal of the proposed study is to rectify this disparity, and provide up-to-date race-specific modules in the FELS method for skeletal maturity assessment. Children of diverse racial/ethnic groups will be included via multiple existing radiographic collections nationwide. The updated method for skeletal maturity assessment will be accomplished through three specific aims. Aim 1 will determine differences between races in both the timing and tempo of skeletal maturity and its individual components. Aim 2 will re-calibrate the FELS method using data from contemporary children. This aim will also provide a new program for assessment of skeletal maturity with sex- and race- specific modules. The program will be user-friendly and open source, with both stand-alone and web-based capability. Aim 3 will integrate two new interpretive parameters into the FELS assessment program output: relative contribution of five maturation categories to skeletal age, and prediction of future catch up or slow- down in skeletal maturation for a given child. The combination of these three aims will serve to benefit the treatment and clinical management of children nationwide.